The problem of maintaining a proper running clearance between braking members is an old one. For many years, drum style brake shoes were manually advanced to compensate for wear of the shoe friction surface, for example, by turning a star wheel adjustment nut. This periodic maintenance routine was frequently initiated upon the vehicle driver detecting excess brake pedal travel. Later, automatic adjusters for resetting the rest or released shoe location were developed, some requiring the vehicle to be braked while moving in reverse to reposition the shoes. With the advent of disc brakes, some systems have employed a radially deformable metal tube with a shoulder which provides a rest or retracted position for the brake pads. Excess pad travel induces radial deformation of the tube axially repositioning the shoulder along the tube and establishing a new pad retracted location. Other systems have relied on the natural resilience of piston seals to retract the brake pads and provide running clearance between the brake rotor and brake pads. In the case of floating caliper style disc bakes, the piston seal resilience adequately retracts the inboard brake pad away from the rotor after a braking event, but repositioning of the outboard pad has been somewhat unreliable. Recent attempts to achieve more uniform clearance for both inboard and outboard pads have concentrated on the interplay between the caliper guide pins and the member in which they slide.
For example, one embodiment in U.S. Pat. No. 5,934,416 employs a plurality of elastic annular rings recessed either in the guide pin surface or the sidewall of the hole in which the guide pin reciprocates. The annular rings engage the other member and deform without slipping during braking. Excess brake pad travel induces slippage between the members after the deformation resulting in repositioning the pin within its hole. In another embodiment, a series of axially spaced apart radially extending springs are located along the pin surface or hole sidewall and the other member has a single similar radially extending spring. During normal braking, the single spring transition between a specific pair of the other member springs, but excess pad travel causes the single spring to slip past one of the two adjacent springs and thereafter to transition between a new specific pair. Variations on these techniques are employed in other embodiments.
U.S. Pat. No. 6,397,983 reiterates stating a common problem in the art of brakes is that stationary brake pads often drag on a movable friction element after the braking pressure has been released. This causes excessive wear on the pads and reduces the overall performance of the vehicle. In the art of automotive and truck disc brakes, this problem is presented when the brake pad that is carried by a movable, or floating, caliper drags on the rotor after braking pressure is released. This occurs mostly because the frictional forces between the elements carrying the caliper, such as the friction between the slide pins and the walls of the bore in which they ride, prevent return of the caliper to a rest position providing a gap between the pad and the rotor after release of braking pressure. This patent suggests a mechanism for providing a clearance between a brake pad and a rotor in a sliding-pin, floating-caliper disc brake which includes a bushing that receives a sliding pin and a resilient element between the end of the pin and the end of the bushing. The bushing is a cylindrical shell with smooth inner and outer diameters for receiving the pin and engaging a bore respectively and has a reduced diameter hole in an otherwise closed end through which a reduced diameter free end portion of the pin passes. A retainer engages the free end and holds a wave washer captive between the bushing end and the free pin end. The pin reciprocates in the bushing during operation of the brakes, and the bushing moves along the bore as the brake pads wear. A large number of parts coupled with complex assembly are just one problem with this solution, thus after over one-half century, these problems remain partially unsolved and continue to plague the industry.
It is desirable to maintain proper running clearance for both inboard and outboard brake pads in a very simplistic and economical manner.